A leading Chinese forensic scientist has publicly cast doubt on the conviction of Gu Kailai for murdering British businessman Neil Heywood with cyanide.

The wife of ousted leader Bo Xilai was convicted and handed a suspended death penalty last month over the death of the 41-year-old Briton in Chongqing last year.

But Wang Xuemei, an official at the Supreme People's Procuratorate, wrote in a blog post on Wednesday night: "I feel very pained, upset and scared that our court believed the theory [Heywood] was poisoned with cyanide."

Wang has had an unusually high media profile in the past, lauded in the Chinese media as the first female forensic scientist to work for the country's highest level prosecution body.

But she told the Guardian that she had been pressing officials to move her from her position for almost a decade because she had an "empty title" with no real duties.

Even so, it is extremely surprising that an official in her position would publicly question the verdict in such a politically sensitive case.

Discussions of the case have been heavily censored online and almost no coverage has appeared in Chinese media beyond reproductions of reports from state news agency Xinhua.

Wang asked why none of the obvious symptoms of cyanide poisoning were cited in the accounts that emerged from Gu's trial or that of the former Chongqing police chief, Wang Lijun.

On Monday a Chinese court sentenced him to 15 years for covering up Heywood's murder, accepting bribes and abuse of power and defection.

One simple explanation may be that few details of the scientific evidence used to convict Gu have emerged, although an unofficial account of her trial from a person in the court said her defence team questioned the scientific evidence against her.

Her lawyers reportedly said Wang Lijun took two blood samples yet found no traces of poison, while a third sample that he took – tested only four months later – found low levels of a toxin, apparently insufficient to kill.

Chinese trials often rely heavily on testimony from the accused and state media have said Gu confessed and to Heywood's murder.

Wang Lijun's trial is also said to have heard a recording the police chief made secretly of Gu confessing to him the day after Heywood's death, though no details were given.

After discussing Gu's mental health problems, including her alleged paranoia, Wang Xuemei also wrote that the 53-year-old trusted the former police chief deeply and added: "In other words, Wang Lijun could easily have used Gu to do whatever he wanted to do.

"Who would benefit from Neil Heywood's death?"

She told the Guardian: "I don't care how long the blog is up there. I just want to tell people I feel humiliated.

"I think Chinese criminal doctors are not such idiots. I have done my duty and fulfilled my historical responsibility."